The present invention relates to a terminal assembly having an externally threaded screw engaged within an internally threaded bore of a terminal, with the screw thread being deformed adjacent to an end remote from the screw head. The deformation acts as a,stop to limit removal of the screw from the terminal bore. Additionally, the present invention relates to a method of forming the terminal assembly.
Wiring for industrial, residential, commercial and other applications for providing access to and controlling the provision of electrical power includes such wiring devices as plugs, receptacles and switches. The various wiring devices are connected by insulated copper wires. The wires are connected to the wiring devices by screw terminals mounted on the wiring devices.
Each screw terminal includes a terminal base having an internally threaded bore and a screw having a shank with an external thread and a head on one end of the shank. The screw shank is threaded into the bore, with a portion of the threaded screw shank extending beyond the end of the bore remote from the screw head. The copper wire ends are secured to the terminal by being located between the terminal base and the underside of the screw head, and are then secured in place by tightening the screw head against the conductor to trap the conductor between the terminal base and the screw head.
To enhance this connection, a backing plate is often provided between the screw head and the terminal base. The backing plate has an opening through which the screw shank extends, and has depending tabs which engage slidably within openings in the terminal base. When backing plates are used, the conductors are located between the backing plates and the terminal bases. With rotation of the backing plates being prevented by the engagement of the backing plate tabs and the terminal base openings, the conductors are compressed without the application of torque resulting from the threading of the screw into the terminal base bore.
When the wiring devices are sold or provided for installation, the screws are backed out of or unthreaded to a predetermined degree in the terminal base bores to provide adequate space between the screw head and the terminal base or between the backing plate and the terminal base to readily receive the conductor without having to unthread the screws. The installer then need only tighten the screws after placing the conductor in the appropriate location to secure the conductor in place to the wiring device.
However, conventional terminal assemblies for wiring devices do not have means for fixing the amount of backout or unthreading of the screws. Without a means for fixing this amount, the screws can be threaded too far into or out of the terminal base bore. If the screws are threaded too far into the terminal base bore, inadequate space is provided for the conductor, requiring the installer to back the screw out of the terminal base. This action requires additional effort by the installer and increases the possibility of the screw becoming removed from the wiring device and becoming lost. Additionally, if the screw is not adequately threaded into the terminal base, the screw can become disconnected from the wiring device and lost.
An object of the present invention is to provide a terminal assembly for a wiring device that enables the screw to be backed out to a predetermined dimension according to a relatively tight tolerance.
Another object of the present invention is to provide a screw terminal which allows the screw to be backed out from the terminal base to its maximum capacity without becoming disengaged, and which is inexpensive and of rugged construction.
A further object of the present invention is to provide a method of making a terminal assembly which is easy to manufacture and provides a terminal assembly which is inexpensive and of rugged construction.
The foregoing objections are obtained by a terminal assembly comprising a terminal base and a screw. The terminal base has a bore with an internal thread. The screw has a shank with opposite first and second ends and with an external thread, and has a head on the first end of the shank. A deformation is provided in a portion of the external thread adjacent the shank second end.
By forming the terminal assembly in this manner, the deformation acts as a stop to limit the degree of removal of the screw from the bore in the terminal base. This allows the backout of the screw to be set to a predetermined dimension with a relatively high tolerance. Additionally, the screw can be backed out to its maximum extent without it becoming disengaged from the terminal base since the deformation prevents unthreading beyond the deformation.
In a particularly advantageous embodiment of the invention, the deformation is formed by a stake in the shank second end. The stake forms the deformation and can be easily formed after the screw is located within the terminal base bore.
The foregoing objects are also basically obtained by a method of forming a terminal assembly comprising the steps of threading an external thread of a shank of a screw into an internally threaded bore in a terminal base. The shank has opposite first and second ends with a head on its first end. A portion of the external thread is deformed adjacent the second end of the shank to limit the amount the screw can be backed out of the bore, after the screw had been threaded into the bore.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.